Method for purification and storage of Til4 for Ti-containing film deposition

ABSTRACT

Disclosed are methods for purification of a crude TiI4 for deposition of Ti-containing films including evaporating volatile impurities in the crude TiI4 under vacuum at room temperature in a sublimator and removing the volatile impurities, placing the sublimator in a hot oil bath under vacuum at a temperature to evaporate TiI4 and form powders or a solid, and sublimating the powers or the solid under vacuum at the temperature to obtain the purified TiI4. Disclosed are methods for storage of a pure TiI4 including drying a stainless-steel canister, instantaneously moving the dried stainless steel canister into a glove box under inert atmosphere at room temperature, moving the pure TiI4 into the glove box, filling the pure TiI4 into the dried stainless-steel canister, and sealing the dried stainless steel canister containing the pure TiI4 with metallic sealing.

TECHNICAL FIELD

Disclosed are methods for purification and storage of a material for deposition of Ti-containing films, in particular, methods for purification and storage of TiI₄ for deposition of Ti-containing films.

BACKGROUND

For semiconductor chip manufacturing, a quality of materials is a key point to maintain constant and high quality of products. Titanium halide compounds, such as TiCl₄ and TiI₄, have been used as materials for deposition of Ti and TiN films in chip manufacturing industries. See, e.g., US2013/0115383 to Xinliang Lu et al.

TiI₄ is very sensitive to the air and its quality needs to be controlled well for its usage in order to keep constant and high performance during manufacturing processes in semiconductors. U.S. Pat. No. 5,700,519 to Lam discloses a method for depositing ultra high purity titanium films by generating gaseous TiI₄ in situ by reacting titanium metal starting material with gaseous iodide in a reaction chamber and purifying the TiI₄ by a double distillation process to produce ultra high purity of greater than 99.998% TiI₄.

A need remains for methods of purifying and storing TiI₄ so that it is of suitable purity for vapor deposition of Titanium-containing films.

SUMMARY

Disclosed are methods for purification of crude TiI₄ for deposition of Ti-containing films, the method comprising the steps of introducing the crude TiI₄ into a sublimator having a cold trap cooled by liquid nitrogen, evaporating volatile impurities in the crude TiI₄ under vacuum at room temperature in the sublimator and collecting the evaporated volatile impurities in the cold trap, removing the volatile impurities, placing the sublimator, after the step of removing the volatile impurities, in a hot oil bath under vacuum at a temperature to evaporate TiI₄ and form powders or a solid in the cold trap of the sublimator, and sublimating the powers or the solid under vacuum at the temperature to obtain the purified TiI₄.

Also disclosed are methods for storage of a pure TiI₄ for deposition of Ti-containing films, the method comprising drying a stainless-steel canister at a temperature more than 100° C. for a period of time, instantaneously moving the dried stainless steel canister into a glove box under inert atmosphere at room temperature, moving the pure TiI₄ into the glove box without any contact with air, filling the pure TiI₄ into the dried stainless-steel canister in the glove box, and sealing the dried stainless steel canister containing the pure TiI₄ with metallic sealing in the glove box.

Notation and Nomenclature

The following detailed description and claims utilize a number of abbreviations, symbols, and terms, which are generally well known in the art. While definitions are typically provided with the first instance of each acronym, for convenience, Table 1 provides a list of the abbreviations, symbols, and terms used along with their respective definitions.

TABLE 1 a or an One or more than one Approximately or ±10% of the value stated about CVD chemical vapor deposition LPCVD low pressure chemical vapor deposition PCVD pulsed chemical vapor deposition SACVD sub-atmospheric chemical vapor deposition PECVD plasma enhanced chemical vapor deposition APCVD atmospheric pressure chemical vapor deposition HWCVD hot-wire chemical vapor deposition Flowable PECVD flowable plasma enhanced chemical vapor deposition MOCVD metal organic chemical vapor deposition ALD atomic layer deposition spatial ALD spatial atomic layer deposition HWALD hot-wire atomic layer deposition PEALD plasma enhanced atomic layer deposition MP melting point TGA thermogravimetric analysis TG-DTA thermogravimetric differential thermal analysis DTA differential thermal analysis PTFE Polytetrafluoroethylene PFA Perfluoroethers

Please note that the films or layers deposited, such as titanium oxide or titanium nitride, may be listed throughout the specification and claims without reference to their proper stoichiometry (i.e., TiO₂, TiO₃, Ti₃N₄). The layers may include pure (Ti) layers, carbide (Ti_(o)C_(p)) layers, nitride (Ti_(k)N_(l)) layers, oxide (Ri_(n)O_(m)) layers, or mixtures thereof, wherein k, l, m, n, o, and p inclusively range from 1 to 6. For instance, titanium oxide is Ti_(n)O_(m), wherein n ranges from 0.5 to 1.5 and m ranges from 1.5 to 3.5. More preferably, the titanium oxide layer is TiO₂ or TiO₃.

Any and all ranges recited herein are inclusive of their endpoints (i.e., purity ranging from 99% w/w to 100% w/w includes a purity of 99% w/w, a purity of 100% w/w, and any purities between the two (i.e., 99.1, 99.2, 99.353, etc.)).

The standard abbreviations of the elements from the periodic table of elements are used herein. It should be understood that elements may be referred to by these abbreviations (e.g., Si refers to silicon, N refers to nitrogen, O refers to oxygen, C refers to carbon, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements.

FIG. 1 is a ThermoGravimetric Analysis (TGA) graph demonstrating the percentage of weight loss with increasing temperature of TiI₄ in air;

FIG. 2 is a ThermoGravimetric-Differential Thermal Analysis (TG-DTA) graph demonstrating the percentage of weight loss (TG) and the differential temperature (DT) with increasing temperature of purified TiI₄;

FIG. 3 is a TG-DTA graph demonstrating the percentage of weight loss (TG) and the differential temperature (DT) with increasing temperature of decomposed TiI₄;

FIG. 4 is a TG-DTA graph demonstrating the percentage of weight loss (TG) and the differential temperature (DT) with increasing temperature of purified TiI₄ stored for one month;

FIG. 5 is a TG-DTA graph demonstrating the percentage of weight loss (TG) and the differential temperature (DT) with increasing temperature of purified TiI₄ isolated from moisture and oxygen for 5 weeks; and

FIG. 6 is a TG-DTA graph demonstrating the percentage of weight loss (TG) and the differential temperature (DT) with increasing temperature of a purified TiI₄ under atmospheric pressure.

DESCRIPTION OF PREFERRED EMBODIMENTS

Disclosed are methods of purifying and maintaining purity of TiI₄ for deposition of Ti-containing films in semiconductor industries.

The quality of TiI₄ for producing Ti-containing films is the key point for deposition of Ti-containing films. To meet this requirement, the purity of TiI₄ should range from approximately 99% w/w to approximately 100% w/w, and preferably greater than 99.9% w/w. The non-volatile impurities of TiI₄ should range from 0% w/w to approximately 1% w/w, preferably less than 0.5% w/w. The amount of I₂ and/or HI contained in TiI₄ should be range from 0% w/w to approximately 1% w/w, preferably less than 0.5% w/w.

The purity of TiI₄ used for the deposition of Ti-containing films is normally guaranteed from suppliers, but other impurities are usually not mentioned. For example, the purity of TiI₄ may be shown as 95% w/w. Due to the stringent requirements for the purity of TiI₄ for deposition of Ti-containing films, the other 5% w/w impurities must be removed.

FIG. 1 is a ThermoGravimetric Analysis (TGA) curve of TiI₄ in air showing the percentage of weight loss with increasing temperature. A TiI₄ sample with a purity of 95% w/w in air was analyzed by TGA. TiI₄ decomposes in air, forming I₂ and/or HI, and TiO_(m)I_(n), wherein 0<m<2 and 0<n<4.

As shown in FIG. 1, part A indicates the presence of I₂ and/or HI in TiI₄ in air and part B indicates the presence of TiO_(m)I_(n) compounds in TiI₄ in air. Since TiI₄ tends to decompose in air, the decomposed compounds of TiI₄ (i.e., I₂, HI and/or TiO_(m)I_(n)) prevent the supply of a constant vapor of TiI₄ when TiI₄ is heated and makes the deposition process unreliable for deposition of Ti-containing films in semiconductor industries. When TiI₄ is purified and the impurities in TiI₄ are removed, TiI₄ evaporates smoothly.

The impurities existing in TiI₄ may include volatile impurities, such as I₂ and/or HI, and non-volatile impurities, such as TiO_(m)I_(n). As such, the purification methods include the steps of evaporating the volatile impurities to remove the volatile impurities and sublimating TiI₄ to separate TiI₄ from the non-volatile impurities, respectively.

The disclosed methods for purification of TiI₄ includes introducing TiI₄ into a sublimator having a cold trap cooled by liquid nitrogen, evaporating volatile impurities in the TiI₄ under vacuum at room temperature in the sublimator and collecting the evaporated volatile impurities in the cold trap, removing the volatile impurities from the cold trap, placing the sublimator, after the step of removing the volatile impurities, in a hot oil bath under vacuum at a temperature to evaporate TiI₄ and form powders or a solid in the cold trap of the sublimator, and sublimating the powders or the solid under vacuum at the temperature to obtain the purified TiI₄.

Herein, the TiI₄ starting material may have a purity ranging from approximately 90% w/w to approximately 95% w/w. The volatile impurities may include I₂ and/or HI. The vacuum placed on the sublimator may range between approximately 1 mTorr (0.13 Pa) to approximately 10 mTorr (1.3 Pa), more preferably between approximately 2 mTorr (0.27 Pa) to approximately 8 mTorr (1.1 Pa). The sublimator is heated to a temperature higher than the melting point of TiI₄, ranging from approximately 150° C. to approximately 190° C.

The purified TiI₄ may have a purity ranging from approximately 99% w/w to approximately 100% w/w, preferably greater than 99.9% w/w. The amount of non-volatile impurities contained in the purified TiI₄ may range from 0% w/w to approximately 1% w/w, preferably less than 0.5% w/w. The amount of I₂ and/or HI contained in the purified TiI₄ may range from 0% w/w to approximately 1% w/w, preferably less than 0.5% w/w. One of ordinary skill in the art will recognize that the purity may be determined by H NMR or gas or liquid chromatography with mass spectrometry.

The disclosed methods for storage of a purified TiI₄ include drying a stainless steel canister at a temperature, ranging from approximately 100° C. to approximately 200° C., for 3 hours to 24 hours, instantaneously moving the dried stainless steel canister into a glove box, moving the purified TiI₄ into the glove box without any contact with air, filling the purified TiI₄ in the dried stainless steel canister in the glove box and sealing the well-dried stainless steel canister containing the purified TiI₄ with metallic sealing. The glove box may be an inert atmosphere glove box operated at room temperature in which moisture level is highly controlled between 0 ppmv and approximately 5 ppmv (dew point −65° C.), preferably less than 1 ppm (dew point −76° C.). The inert gas may be selected from N₂ or Ar. The dried stainless steel canister may be moved into the glove box promptly after drying without exposure to the air for a long time to avoid water re-condensation on the stainless steel canister.

A dried stainless steel canister with metallic sealing is suitable for storing TiI₄. Other materials, such as Plastic, PTFE, PFA, may contain moisture and it is difficult to remove moisture from these materials by heating. As a result, any material from which it is difficult to remove moisture is not preferred as a component of the storage vessel, including any sealing and capping parts.

FIG. 2 is a Themogravimetric-Differential Thermal Analysis (TG-DTA) curve of a purified TiI₄ after removing impurities. The purified TiI₄ sample has a purity of 95% w/w TiI₄. As shown in FIG. 2, the melting point (150° C.) of TiI₄ is indicated as peak C in a DTA curve.

However when the purified TiI₄ sample is stored with a small amount of moisture, the purified TiI₄ sample starts decomposing and new DTA peak D appeared at lower temperature (126° C.) than the melting point C (150° C.), as shown in FIG. 3. FIG. 3 is a TG-DTA curve of decomposed TiI₄. Although the TG curve of TiI₄ does not change comparing to the purified TiI₄, generation of impurities is observed (e.g., peak D). Purifying the decomposed TiI₄ sample one more time, the peak D in the TG-DTA curve disappears.

Alternatively, when the purified TiI₄ sample is stored away from moisture and oxygen, the peak D in the TG-DTA curve does not appear after long term storage, for example, one month, as shown in FIG. 4. FIG. 4 is a TG-DTA curve of a purified TiI₄ stored for one month. The peak D does not appear in FIG. 4, even when the TiI₄ sample is heated in well-closed canister at 140° C. As long as the purified TiI₄ sample is isolated from moisture and oxygen, the peak D does not appear after several weeks, e.g., 5 weeks, so that the quality of TiI₄ is retained. FIG. 5 is a set of TG-DTA curves of a purified TiI₄ stored isolated from moisture and oxygen for 5 weeks. As shown in FIG. 5, there is no extra impurity peak generated during the 5 weeks.

EXAMPLES

The following non-limiting examples are provided to further illustrate embodiments of the invention. However, the examples are not intended to be all inclusive and are not intended to limit the scope of the inventions described herein.

Example 1 Purification of Crude TiI₄

TiI₄ (25 g) was purified by sublimation under vacuum in a sublimator. The sublimator has a cold trap, or finger, cooled by liquid nitrogen. When vacuum (e.g., 8 mTorr or 1.1 Pa) was applied to the apparatus at room temperature, volatile impurities started to sublime and were collected in the cold trap. The volatile impurities include I₂ and/or HI.

After all volatile impurities were removed, the apparatus was then immersed in a hot oil bath at 180° C. and under vacuum, for example, 2-6 mTorr. Dark brown powder or a solid was formed and attached on the cold trap of the apparatus. The dark brown powder or the solid was collected and purified one more time by sublimation at 180° C. at 2-6 mTorr. Then pure TiI₄ (˜21.9 g) was obtained yielding 87.6% w/w of pure TiI₄.

Example 2 Measurement of Purity

The purified TiI₄ was analyzed by TG-DTA under atmospheric pressure (e.g., 1010 mbar or 101 kPa). Purge gas was Nitrogen at 220 sccm. Pan was Al. FIG. 2, FIG. 4 and FIG. 5 are the exemplary TG-DTA curves of a purified TiI₄ at different time periods after purification.

Example 3 Storage of Purified TiI₄

The purified TiI₄ is air sensitive and contamination by even a small amount of moisture and oxygen is not acceptable. The purified TiI₄ should be stored in a dried stainless steel (SS) canister or tube with metallic sealing.

The stainless steel canister was dried at 125° C. for at least 3 hours. The dried stainless steel canister instantaneously was moved into an inert atmosphere (e.g., Ar) glove box without exposure to the air for a long time to avoid water re-condensation on the stainless steel canister. Moisture level in the glove box was highly controlled for less than 5 ppmv. The purified TiI₄ was moved into the glove box without any contact with air and then filled in the dried stainless steel canister in the glove box. The dried stainless steel canister containing the purified TiI₄ was then sealed with metallic sealing.

Example 4 Example for Usage of TiI₄

The purified TiI₄ may be used for Ti-containing film deposition, preferably Ti and TiN film depositions.

The disclosed purified TiI₄ may be used to deposit Ti-containing films using any deposition methods known to those of skill in the art. Examples of suitable deposition methods include chemical vapor deposition (CVD) or atomic layer deposition (ALD). Exemplary CVD methods include thermal CVD, pulsed CVD (PCVD), low pressure CVD (LPCVD), sub-atmospheric CVD (SACVD) or atmospheric pressure CVD (APCVD), hot-wire CVD (HWCVD, also known as cat-CVD, in which a hot wire serves as an energy source for the deposition process), radicals incorporated CVD, plasma enhanced CVD (PECVD) including but not limited to flowable PECVD, and combinations thereof. Exemplary ALD methods include thermal ALD, plasma enhanced ALD (PEALD), spatial isolation ALD, hot-wire ALD (HWALD), radicals incorporated ALD, and combinations thereof. Super critical fluid deposition may also be used. The deposition method is preferably ALD, PE-ALD, or spatial ALD in order to provide suitable step coverage and film thickness control.

The disclosed purified TiI₄ may be used to deposit Ti-containing films with a co-reactant. The co-reactant may be selected from H₂, NH₃, AlMe₃, AlEt₃, AliBu₃, HAlMe₂, H₃AlNEt₂Me, H₃AlNMe₃, (BH₄)AlH₂NMe₃, H₃Al(Me-NC₄H₈), other alanes, SiH₄, Si₂H₆, Si₃H₈, (CH₃)₂SiH₂, (C₂H₅)₂SiH₂, (CH₃)SiH₃, (C₂H₅)SiH₃, phenyl silane, N₂H₄, N(SiH₃)₃, N(CH₃)H₂, N(C₂H₅)H₂, N(CH₃)₂H, N(C₂H₅)₂H, N(CH₃)₃, N(C₂H₅)₃, (SiMe₃)₂NH, (CH₃)HNNH₂, (CH₃)₂NNH₂, phenyl hydrazine, N-containing molecules, B₂H₆, 9-borabicyclo[3,3,1]nonane, dihydrobenzofuran, pyrazoline, triethylaluminum, triethylaluminum, dimethylzinc, diethylzinc, radical species thereof, and mixtures thereof. Preferably, the reducing agent is H₂, NH₃, SiH₄, Si₂H₆, Si₃H₈, SiH₂Me₂, SiH₂Et₂, N(SiH₃)₃, or their mixtures.

Additionally, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances.

While embodiments of this invention have been shown and described, modifications thereof may be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and not limiting. Many variations and modifications of the composition and method are possible and within the scope of the invention. Accordingly the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims. 

We claim:
 1. A method for purification of TiI₄ for deposition of Ti-containing films, the method comprising the steps of: introducing TiI₄ into a sublimator having a cold trap cooled by liquid nitrogen; evaporating volatile impurities in the TiI₄ under vacuum at room temperature to produce semi-purified TiI₄ and collecting the evaporated volatile impurities in the cold trap; removing the evaporated volatile impurities from the cold trap; placing the sublimator containing the semi-purified TiI₄ in a hot oil bath under vacuum at a temperature to evaporate TiI₄ and form a powder or solid in the cold trap; and sublimating the powder or solid under vacuum at the temperature to obtain the purified TiI₄.
 2. The method of claim 1, wherein the crude TiI₄ has a purity ranging from approximately 90% w/w to approximately 95% w/w.
 3. The method of claim 1, wherein the temperature ranges from approximately 150° C. to approximately 190° C.
 4. The method of claim 3, wherein the temperature is 180° C.
 5. The method of any claim of 1, wherein the volatile impurity is I₂.
 6. The method of any claim of 1, wherein the volatile impurity is HI.
 7. The method of claim 1, wherein the purified TiI₄ has a purity of 99% w/w.
 8. The method of claim 1, wherein the purified TiI₄ has a purity ranging from approximately 99% w/w to approximately 100% w/w.
 9. The method of claim 1, wherein the purified TiI₄ has a purity ranging from approximately 99.9% w/w to approximately 100.0% w/w.
 10. The method of claim 1, wherein the purified TiI₄ contains between 0% w/w and approximately 1% w/w non-volatile impurities.
 11. The method of claim 1, wherein the purified TiI₄ contains between 0% w/w and approximately 0.5% w/w non-volatile impurities.
 12. The method of claim 1, wherein the purified TiI₄ contains between 0% w/w and approximately 1% w/w I₂ and/or HI.
 13. The method of claim 1, wherein the purified TiI₄ contains between 0% w/w and approximately 0.5% w/w I₂ and/or HI. 